1. Field of the Invention
The present invention relates to a high-speed puffer-type earthing switch.
2. Description of the Related Art
Conventional puffer-type earthing switches have a slit on a lever of a guide cylinder with the aim of lowering the operating energy when driving the guide cylinder. The slit begins from an end of the lever of the guide cylinder and extends up to the halfway of the piston stroke range. When a movable contact retreats up to a predetermined position in the course of opening an earthing switch, insulating gas stored in the guide cylinder leaks through the slit, thereby causing the pressure in the guide cylinder to become equal to the surrounding atmospheric pressure. In consequence, operating energy is lowered in the latter half cycle of the opening operation. For details, refer to the Japanese Patent Application Laid-Open No. H05-114337 for example.
High-speed puffer-type earthing switches are used in ultra-high voltage transmission lines, which dealing with 1000 KV for example, to prevent the transmission lines from being disconnected when earthing occurs accidentally. Specifically, one high-speed puffer-type earthing switch is arranged on each end of the transmission line to forcibly cancel the secondary arc current that is produced when the earth current is cut off to enable the transmission line to be closed again at a high speed.
In the conventional puffer-type earthing switches in the latter half cycle of an actuating operation, load remained as it was without causing the operating energy to be lowered at all. On the other hand, in the high-speed puffer-type earthing switches, although the current breaking performance is important, it is more important that the duty of short-circuit actuating performance be satisfied during an actuating operation. In other words, higher arc-cancelling capability at an appropriate location and faster actuating speed are concurrently required in the high-speed puffer-type earthing switches.